Lubricating oil composition for internal combustion engines (LAW651)

Abstract

A synthetic lubricating oil composition for internal combustion engines, comprises an organomolybdenum compound, a zinc dithiophosphate and a base stock obtained by blending an ester having a kinematic viscosity of from 8 cSt to 35 cSt at 100° C. and a saponification value of 200 mg-KOH/g or smaller with a poly (alpha-olefin) and/or a highly-refined mineral oil.

Description

This invention relates to a lubricating oil composition for internal combustion engines, and more specifically to an ester-blended lubricating oil composition for internal combustion engines, which makes use of a blended base stock composed of an ester and a poly (.alpha.-olefin) and / or a highly-refined mineral oil and allows a molybdenum-containing friction modifier to show its effects to maximum extent.DESCRIPTION OF THE PRIOR ARTFor a lubricating oil for internal combustion engines of automotive vehicles or the like, which may hereinafter be called the "engine oil", diversified performance is required such as cooling of an inside of an engine, cleaning and dispersion of combustion products, and also prevention of rusting and corrosion in addition to lubrication of piston rings and a cylinder lining, bearings for a crankshaft and connecting rod, and a valve-operating mechanism including cams and valve lifters.Moreover, keeping in step with the recent move toward internal combustio...

AI Technical Summary

Benefits of technology

ous other additives insofar as the advantageous effects of the present invention are not impaired. It is possible to add additives effective for imparting improved properties and performance required for lubricating oils for internal combustion engines, for example, viscosity index improvers, pour-point depressants, oxidation inhibitors, ashless dispersants, wear inhibitors, rust preventives, and the like.

Illustrative examples of the viscosity index improvers can include polymethacrylates, polyisobutylenes, ethylene-propylene copolymers, and hydrogenated styrene-butadiene copolymers. The lubricating oil composition of the present invention for internal combustion engines has good viscosity characteristics by itself so that the addition of a viscosity index improver is not absolutely needed. Nonetheless, a viscosity index improver can be added as desired. When used in racing engines, however, it should be added in an amount smaller than a usual amount, for example, in an amount of 10 wt % or less, preferably 7 wt % or less, more preferably 5 wt % or less to suppress coking.

Illustrative examples of the oxidation inhibitors include amine-type oxidation inhibitors such as alkylated diphenylamines, phenyl-.alpha.-naphthylamines and alkylated .alpha.-naphthylamines; hindered phenolic oxidation inhibitors such as 2,6-di-t-butylphenol, 2,6-di-t-butylparacresol and 4,4'-methylenebis (2,6-di-t-butyl-phenol); phosphorus-containing oxidation inhibitors; and sulfur-containing oxidation inhibitors such as monosulfides and polysulfides. They can be used normally in a proportion of from 0.05 wt % to 2 wt %.

Illustrative examples of the ashless dispersants include polyalkenyl-succinimides and boron-containing polyalkenylsucccinimides. They can be used in a proportion of from 1 wt % to 10 wt %.

The present invention has been described in detail above. As preferred embodiments of the present invention, synthetic lubricating oil compositions for internal combustion engines, said compositions being of the following formulas and properties, can be furnished.

Lubricating oil compositions of this invention for internal combustion engines, which have been prepared as described above, can withstand particularly severe use conditions and are hence suited for racing cars.

Problems solved by technology

Moreover, keeping in step with the recent move toward internal combustion engines of higher performance and higher output for automotive vehicles, sliding parts are exposed to ever increasing more severe friction and abrasion conditions at high temperatures, leading to a demand for a lubricating oil capable of withstanding such extremely severe conditions.

However, molybdenum-base friction modifiers carry with them the problems that they show extremely low friction reducing effects when used in combination with ester-blended base stocks and that the effects of molybdenum-base friction modifiers are substantially reduced in the presence of a phosphorus component such as a zinc dithiophosphate, especially in the presence of such a phosphorus component at a high concentration.

As has been explained above, there is a significant obstacle involved with the use of ester-blended base stocks as lubricating oils for internal combustion engines, said lubricating oils being required to have friction reducing effects, although they are excellent in oxidation stability, cleaning and dispersion ability and the like.

A saponification value higher than 200 mg-KOH / g cannot exhibit the friction reduction effects of the molybdenum-base friction modifier, so that the coefficient of friction is not lowered sufficiently.

On the other hand, a saponification value lower than 80 mg-KOH / g leads to an increase in the coefficient of friction at a high oil temperature, thereby making it difficult to achieve the object, namely, a saving in fuel consumption.

An ester content lower than 10 wt % carries with it a potential problem that the coefficient of friction may increase at high temperatures, and on the other hand, an ester content higher than 30 wt % tends to cause a problem such that the friction reducing effect of the organomolybdenum compound may be impaired.

If the content does not reach 100 ppm, the friction reducing effect is not sufficient.

On the other hand, even if the content exceeds 1,000 ppm, the friction reducing effect is not available to such an extent as corresponding to the increased content.

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